A multi-input multi-output (MIMO for short) technology is introduced in a Long Term Evolution (LTE for short) system and a Long Term Evolution Advanced (LTE-A for short) system, and the MIMO technology plays an important role in increasing a system throughput. In the MIMO technology, compared with an open-loop MIMO transmission scheme, a closed-loop MIMO transmission scheme can bring a larger capacity increase. The closed-loop MIMO transmission scheme refers to: A downlink is used as an example. A base station (BS for short) sends a measurement pilot. Then, after receiving the measurement pilot, a terminal enables, in an uplink feedback manner, the base station to obtain a characteristic of a downlink channel of each terminal, so as to select a precoding scheme that is more suitable for an instantaneous channel characteristic. In this process, the base station sends the measurement pilot, and a process in which after estimating the measurement pilot, the terminal enables, in the uplink feedback manner, the base station to obtain a channel characteristic is referred to as channel obtaining.
Currently, a type of channel obtaining method in a protocol standard of LTE or a protocol standard of LTE-A is as follows: First, during a development stage of the protocol standard, vectors that can quantize channel space are designed according to frequently-used antenna forms and permanently included in the protocol standard, and these vectors are referred to as a codebook; then, a base station sends a measurement pilot in actual communication, and a terminal in a cell measures the pilot to quantize an actual channel according to the codebook in the protocol and selects an optimal group of codebook indexes to be fed back to the base station. This channel obtaining method is referred to as a channel obtaining method based on codebook feedback.
Codebook design in a current protocol standard is designed based on an antenna with a specific form. However, ever-increasing maturation of a large-scale antenna technology and more complicated and diversified application scenario requirements of future 5G raise a new challenge to codebook design. First, future antenna forms are more diversified and extend from a conventional linear array to a planar array and even a spheroidal array. Second, different antenna beam coverage requirements appear because of diversity of application scenarios of future 5G. For example, in a coverage scenario of some skyscrapers, a base station needs to implement refined beam division in a vertical direction in a beam range. In some large-scale venues, a base station needs to implement refined beam division in a horizontal direction.
It is learned from the foregoing analysis that, an application requirement of future 5G poses a new challenge to a MIMO technology. However, a codebook designed based on a single antenna form in 3GPP specifications obviously cannot satisfy quantization of channel space in different antenna forms, and cannot meet requirements of different application scenarios.